Scheduling energy harvesting nodes in a wireless sensor networks

ABSTRACT

A system and method for optimizing power consumption of energy harvesting nodes in a wireless sensor network. In one embodiment, a system includes a network coordinator. The network coordinator includes a wireless transceiver and a controller. The wireless transceiver is configured to provide access to the wireless sensor network. The controller is configured to determine whether a wireless device that is wirelessly communicating with the network coordinator is powered via energy harvesting. The controller is also configured to schedule, based on a determination that the wireless device is powered via energy harvesting, the wireless device to communicate via the wireless sensor network using a priority timeslot of a superframe of the wireless sensor network. The priority timeslot is a timeslot occurring in an initial portion of the superframe.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/557,002, filed on Aug. 30, 2019, which is a continuation of U.S.patent application Ser. No. 13/951,839, filed on Jul. 26, 2013, now U.S.Pat. No. 10,405,326, which claims the benefit of U.S. Provisional PatentApplication No. 61/678,313, filed on Aug. 1, 2012, each of which isincorporated by reference herein in its entirety.

BACKGROUND

Wireless sensor networks (WSNs) are used in a variety of applications,including industrial process monitoring and control, environmentmonitoring, military systems, traffic monitoring, health care, etc. Ingeneral, it is desirable for the sensor nodes of a WSN to operate afterdeployment for as long as possible. Many sensor nodes are batterypowered, and the operating life of the sensor node is limited by thelife of the battery. To overcome this limitation, in an increasingnumber of WSN applications, sensor nodes are powered via harvesting ofambient energy such as wind, solar, thermal, vibration or radiofrequency (RF). The amount of energy available from energy harvesting,at a given time, may be small relative to that available from a battery.

SUMMARY

Various systems and methods for optimizing power consumption of energyharvesting nodes in a wireless sensor network (WSN) are disclosedherein. In some embodiments, a method includes determining, by a networkcoordinator in the WSN, whether a wireless device that is wirelesslycommunicating with the network coordinator is powered via energyharvesting. Based on a determination that the wireless device is poweredvia energy harvesting, the network coordinator schedules the wirelessdevice to communicate via the WSN using a priority timeslot of asuperframe in the WSN. The priority timeslot is a timeslot occurring inan initial portion of the superframe.

In accordance with at least some embodiments, a system includes awireless device powered via energy harvesting and a network coordinatorconfigured to manage access to a WSN. The network coordinator furthercomprises a controller configured to determine whether the wirelessdevice is powered via energy harvesting and schedule, based on adetermination that the wireless is powered via energy harvesting, thewireless device to communicate via the WSN using a priority timeslot ofa superframe of the WSN. The priority timeslot is a timeslot occurringin an initial portion of the superframe.

In accordance with yet other embodiments, a network coordinator includesa wireless transceiver and a controller. The wireless transceiver isconfigured to provide access to the WSN. The controller is configured todetermine whether a wireless device that is wirelessly communicatingwith the network coordinator is powered via energy harvesting. Thecontroller is also configured to schedule, based on a determination thatthe wireless device is powered via energy harvesting, the wirelessdevice to communicate via the WSN using a priority timeslot of asuperframe of the WSN. The priority timeslot is a timeslot occurring inan initial portion of the superframe.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the invention,reference will now be made to the accompanying drawings in which:

FIG. 1 shows a block diagram of an illustrative wireless sensor networkin accordance with various embodiments;

FIG. 2 shows a block diagram of a network coordinator for a wirelesssensor network in accordance with various embodiments;

FIG. 3 shows a block diagram of a wireless sensor node for use in awireless sensor network in accordance with various embodiments;

FIG. 4 shows an illustrative superframe for wireless communication in anetwork in accordance with various embodiments;

FIG. 5 shows a flow diagram for a method for scheduling wireless sensornodes in a wireless sensor network in accordance with variousembodiments; and

FIG. 6 shows a flow diagram for a method for accessing a wireless sensornetwork in accordance with various embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” Also, the term “couple” or “couples” is intended tomean either an indirect or direct electrical connection. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections. The recitation “based on”is intended to mean “based at least in part on.” Therefore, if X isbased on Y, X may be based on Y and any number of other factors.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

In order to effectively utilize an energy harvesting node in a wirelesssensor network (WSN), the power consumption of an energy harvesting nodeshould be minimized. Embodiments of the present disclosure reduce thetime spent by a wireless node powered by energy harvesting in anoperating power state, and increase the sleep time of the node, byidentifying the node as being powered by energy harvesting andscheduling network communication to reduce overall node activity time.Thus, embodiments disclosed herein include identification and schedulingthat provide improved efficiency in the energy utilization of wirelessdevices powered via energy harvesting.

FIG. 1 shows a block diagram of an illustrative wireless sensor network100 in accordance with various embodiments. The network 100 includes anetwork coordinator 108 and a plurality of wireless sensor nodes (102,104, 106), also referred to as wireless sensor devices or simply, sensornodes. Wireless sensor nodes 102-106 detect a condition of theenvironment in which they are disposed, and wirelessly communicateinformation indicative of the sensed environment to the networkcoordinator 108. Each wireless sensor node may communicate withneighboring wireless sensor nodes to form an ad-hoc network in which awireless sensor node repeats transmissions received from other sensornodes to relay data through the network 100.

The network coordinator 108 may be configured to manage the sensor nodes102-106, collect and analyze data received from sensor nodes 102-106,and connect network 100 with a wide area network (WAN) for remote dataaccess. The network coordinator 108 receives measurements and otherinformation transmitted by the sensor nodes 102-106, and may providecontrol information to the sensor nodes 102-106. While, as a matter ofconvenience, FIG. 1 shows only three sensor nodes 102-106 and a singlenetwork coordinator 108, in practice, the network 100 may include anynumber of sensor nodes and coordinators. Each of the sensor nodes102-106 may be powered via variety of different power sources, includingbut not limited to alternating current (AC), a battery, or an energyharvesting subsystem.

Energy harvesting or energy scavenging is a process by which energy isderived from ambient sources (e.g., wind, solar power, thermal energy,salinity gradients, radio frequency (RF), vibration, kinetic energy,etc.), captured, and/or stored. Devices powered via energy harvestingmay be provided with only a small amount of power by an energyharvesting subsystem. At least some of the sensor nodes 102-106 arepowered by energy harvesting.

FIG. 2 shows a block diagram of the network coordinator 108 configuredto manage wireless sensor nodes 102-106 within the WSN 100 in accordancewith various embodiments. The network coordinator 108 includes acontroller 200, a wireless transceiver 202, volatile memory 204,non-volatile memory 206, and an energy source 208. The controller 200may be a general-purpose microprocessor or other instruction executiondevice suitable for use in the network coordinator 108. The volatilememory 204 may be a semiconductor random access memory (RAM), such asstatic RAM (SRAM), or other volatile memory suitable for use in thenetwork coordinator 108. The non-volatile memory 206 may be a FLASHmemory, electrically erasable programmable read-only memory (EEPROM),ferroelectric RAM (FRAM), or other non-volatile memory suitable for usein the network coordinator 108. The energy source 208 provides power tooperate the controller 200, the memories, 204, 206, and other componentsof the network coordinator 108. The energy source 208 may include abattery, an energy harvesting system, and/or other power source suitablefor use in the network coordinator 108.

The transceiver 202 provides communication via a wireless network. Thetransceiver 202 is coupled to the controller 200, and providesinformation received via the wireless network to the controller 200. Forexample, the transceiver 202 may provide to the controller 200, valuesmeasured by the sensor nodes 102-106, sensor node identificationinformation, and other information received via the wireless network.

The controller 200 processes the information received to providemanagement of the wireless network. For example, the controller 200 mayprovide scheduling services that determine when each of the sensor nodes102-106 may communicate via the wireless network. Embodiments of thecontroller 200 schedule sensor node access to the wireless networkbased, at least in part, on the type of energy source powering eachsensor node 102-106. The controller 200 may receive informationidentifying the energy source powering a sensor node via the wirelessnetwork.

FIG. 3 shows a block diagram of the wireless sensor node 102. The blockdiagram may also be applicable to nodes 104, 106, and other wirelessdevice communicating via the wireless network 100. The sensor node 102includes a transceiver 304 and an energy source 306, and may alsoinclude one or more transducers 300. In some embodiments, the energysource 306 includes an energy harvesting subsystem. The sensor node 102also provides information indicating whether the sensor node 102 ispowered via energy harvesting. For example, the sensor node 102 mayprovide a flag that indicates whether the sensor node 102 is powered byenergy harvesting, and wirelessly transmit the flag to the coordinator108. The sensor node 102 may include a processor or other logic thatcontrols operation of the node 102, constructs packets for transmission,parses received transmissions, etc.

The transducers 300 detect conditions in the environment of the wirelesssensor node 102 and provide measurements of the conditions to thenetwork coordinator 108. For example, embodiments of the sensor node 102may measure temperature, pressure, electrical current, humidity, or anyother parameter associated with the environment of the wireless sensor102.

The transceiver 304 converts signals between electrical andelectromagnetic forms to enable the wireless sensor node 102 towirelessly communicate with the sensor nodes 104 and 106, the networkcoordinator 108, and other nodes in the WSN 100.

To minimize power consumption of sensor nodes powered via energyharvesting, embodiments of the network 100 employ a Time DivisionMultiple Access (TDMA) scheduling technique that can reduce the timethat an energy harvesting node is in an operating power mode, andincrease the time spent by the node in a reduced power mode. Thedisclosed scheduling mechanism may be applied in conjunction withnetworking protocols such as those defined by the IEEE802.15.4e standardor other networking protocols or standards.

As noted herein, sensor node 102 provides wireless transmissionsincluding information specifying the energy source powering the node102. The coordinator 108 extracts the information from the wirelesstransmissions that indicates what type of energy source is powering thesensor node 102, and schedules the sensor node 102 powered via energyharvesting, also referred to as an energy harvesting node, to connect tothe WSN 100 in one or more priority timeslots. More particularly, thecontroller 200 schedules the sensor node 102, and other sensor nodesdetermined to be powered via energy harvesting, to communicate usingtimeslots occurring in an initial portion of a superframe, where theinitial or early timeslots of a superframe are referred to as prioritytimeslots.

FIG. 4 shows an illustrative superframe 400 for wireless communicationin the network 100. The superframe 400 includes multiple timeslots(e.g., 402) of equal length. The network coordinator 108 manages thenetwork 100 and defines the superframe.

In conventional wireless networks, allocation of timeslots for use by asensor node does not take into account the power source providing energyto the sensor node. Accordingly, for a sensor node powered via energyharvesting, communication may be scheduled, by the coordinator 108, tooccur in a late portion of timeslots in a superframe (i.e., near the endof the superframe). At the beginning of the superframe 400, each sensornode begins checking each timeslot of the superframe to determinewhether the timeslot is active (i.e., whether the node needs to activatethe radio for communication). The node continues checking timeslotsuntil it has finished checking all slots of the superframe allocated tothe node as well as slots of the superframe shared by all the othernodes. Thereafter, the node can enter sleep mode until the start of thenext superframe. Because the node remains in an operating power modeuntil all timeslots allocated to the node and the shared timeslots havepassed, the limited power provided by energy harvesting may makepowering the node problematic in conventional networks.

Referring again to FIG. 4, as disclosed above, the controller 200 of thecoordinator 108, extracts, from the wireless transmissions of the sensornodes 102-106, information indicating whether the sensor nodes arepowered via energy harvesting. If the information extracted by thecontroller 200 indicates that the senor node 102 is being powered viaenergy harvesting, then, the controller 200 schedules the sensor node102 to communicate during the early (i.e., priority) timeslots of thesuperframe and schedules other sensor nodes, not powered via energyharvesting, to communicate in the later timeslots of the superframe.After the timeslots of the superframe allocated to the sensor node 102have elapsed, the energy harvesting node 102 can transition from anoperating power mode to a low power mode until the start of the nextsuperframe. At the start of the next superframe, the energy harvestingnode 102 transitions from the low power mode to the operating power modeand checks each timeslot. Thus, the time during which an energyharvesting node is in a low power mode (e.g., sleep mode) is maximized,which in turn reduces the energy consumption of the energy harvestingnodes.

FIG. 5 shows a flow diagram for a method 500 for scheduling, by anetwork coordinator, wireless sensor nodes in a wireless sensor networkin accordance with various embodiments. Though depicted sequentially asa matter of convenience, at least some of the actions shown can beperformed in a different order and/or performed in parallel.Additionally, some embodiments may perform only some of the actionsshown. In some embodiments, at least some of the operations of themethod 500, as well as other operations described herein, can beimplemented as instructions stored in computer readable medium andexecuted by a processor (e.g., controller 200).

In block 502, a wireless node (e.g., node 102) is attempting to connectto the wireless sensor network 100, and transmits, to the networkcoordinator 100, a packet including information indicating whether thenode 102 is powered via energy harvesting. In some embodiments, theinformation may include a flag value specifying whether the node 102 ispowered by energy harvesting. The controller 200 of the networkcoordinator 108 extracts the information specifying whether the node 102is powered by energy harvesting from the received packet, and, in block504, examines the information to determine whether the wireless node 102is powered via energy harvesting.

If the node 102 is powered by energy harvesting, then in block 506, thecontroller 200 in the network coordinator 108 schedules the node 102 tocommunicate in a priority timeslot of a superframe of the network 100.

However, if the controller 200 determines, based on the extractedinformation, that the node is not powered via energy harvesting, then,in block 508, the controller 200 schedules the node to communicate in alater timeslot of the superframe. The priority timeslot assigned to anode powered by energy harvesting is earlier in the superframe than thelater timeslot assigned to a node not powered by energy harvesting.

In some embodiments, the coordinator 108 may allocate a prioritytimeslot to an energy harvesting node by reassigning a timeslotcurrently assigned to a non energy harvesting node to an energyharvesting node, and assigning a later timeslot to the non energyharvesting node.

FIG. 6 shows a flow diagram for a method 600, for accessing a wirelesssensor network and communicating via the wireless network in accordancewith various embodiments. Though depicted sequentially as a matter ofconvenience, at least some of the actions shown can be performed in adifferent order and/or performed in parallel. Additionally, someembodiments may perform only some of the actions shown. In someembodiments, at least some of the operations of the method 600, as wellas other operations described herein, can be implemented as instructionsstored in computer readable medium and executed by a processor.

In block 602, the node 102 detects the start of a superframe. Responsiveto detecting the start of the superframe, in block 604, the node 102transitions from a low power state to an operating power state in orderto determine when timeslots allocated to the node 102 for communication(i.e., active timeslots) are occurring.

In block 606, if the node 102 identifies a timeslot as being active,then the node 102 turns its radio on in block 608, and maintains theradio in the on state until all timeslots of the current superframeallocated to the node 102 have elapsed in block 610. If the node 102does not identify an active timeslot in block 606, the node 102 turnsits radio off in block 614.

When all timeslots of the current superframe allocated to the node 102have elapsed, the node 102 transitions from an operating power mode to alow power mode in block 612, and remains in the low power mode until thestart of the next superframe. Because the timeslots allocated to anenergy harvesting node may occur near the start of the superframe,embodiments increase the time spent in the low power mode relative toconventional systems.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A network device comprising: a transceiver; aprocessor coupled to the transceiver; and a non-transitory memorycoupled to the processor and storing instructions that, when executed,cause the processor to allocate of a set of timeslots among a set ofnodes by: receiving, via the transceiver, a communication from a firstnode of the set of nodes that includes a flag indicating that the firstnode is powered by energy harvesting; determining a set of prioritytimeslots within the set of timeslots; allocating a first timeslot ofthe set of priority timeslots to the first node based on the flag;communicating, via the transceiver, allocation of the first timeslot tothe first node; allocating a second timeslot that is not in the set ofpriority timeslots to a second node of the set of nodes; andcommunicating, via the transceiver, allocation of the second timeslot tothe second node.
 2. The network device of claim 1, wherein the set ofpriority timeslots is earliest in the set of timeslots.
 3. The networkdevice of claim 1, wherein the allocating of the first timeslot to thefirst node is such that the first timeslot is prior to any timeslot ofthe set of timeslots allocated to any node of the set of nodes that isnot powered by energy harvesting.
 4. The network device of claim 1,wherein the communication from the first node is a request to join anetwork.
 5. The network device of claim 1, wherein: the communicationfrom the first node is a first communication; the flag is a first flag;and the allocating of the second timeslot that is not in the set ofpriority timeslots to the second node is based on not receiving a secondcommunication from the second node that includes a second flag thatindicates that the second node is powered by energy harvesting.
 6. Thenetwork device of claim 1, wherein the flag that indicates that thefirst node is powered by energy harvesting indicates that the first nodeis powered by at least one of: wind, solar, vibration, radio frequency,or thermal energy.
 7. The network device of claim 1, wherein thetransceiver is a wireless transceiver.
 8. The network device of claim 1,wherein the set of timeslots is associated with an ad-hoc wirelessnetwork for communication between the set of nodes.
 9. The networkdevice of claim 8, wherein the non-transitory memory stores furtherinstructions that, when executed, cause the processor to communicativelycouple the ad-hoc wireless network to a wide area network.
 10. Thenetwork device of claim 1, wherein the first node and the second nodeare wireless sensor nodes.
 11. A method comprising: receiving acommunication from a first node of a set of nodes that includes a flagindicating that the first node is powered by energy harvesting; andallocating a set of timeslots among the set of nodes, wherein the set oftimeslots includes a set of priority timeslots, and wherein theallocating of the set of timeslots includes: allocating a first timeslotof the set of priority timeslots to a first node of the set of nodesbased on the flag; communicating allocation of the first timeslot to thefirst node; allocating a second timeslot that is not in the set ofpriority timeslots to a second node of the set of nodes; andcommunicating allocation of the second timeslot to the second node. 12.The method of claim 11, wherein the set of priority timeslots is theearliest timeslots in the set of timeslots.
 13. The method of claim 11,wherein the allocating of the first timeslot to the first node is suchthat the first timeslot is prior to any timeslot of the set of timeslotsallocated to any node of the set of nodes that is not powered by energyharvesting.
 14. The method of claim 11, wherein the communication fromthe first node is a request to join a network.
 15. The method of claim11, wherein: the communication from the first node is a firstcommunication; the flag is a first flag; and the allocating of thesecond timeslot that is not in the set of priority timeslots to thesecond node is based on not receiving a second communication from thesecond node that includes a second flag that indicates that the secondnode is powered by energy harvesting.
 16. The method of claim 11,wherein the flag that indicates that the first node is powered by energyharvesting indicates that the first node is powered by at least one of:wind, solar, vibration, radio frequency, or thermal energy.
 17. Themethod of claim 11, wherein the set of timeslots is associated with anad-hoc wireless network for communication between the set of nodes. 18.The method of claim 17 further comprising communicatively coupling thead-hoc wireless network to a wide area network.
 19. A method comprising:providing, via a transceiver of a device, a first communication thatincludes a flag indicating that the device is powered by energyharvesting; receiving, via the transceiver, an allocation of a firsttimeslot for communication over a network; receiving a sensormeasurement via a transducer; and providing a second communication thatindicates the sensor measurement during the first timeslot.
 20. Themethod of claim 19, wherein: the first timeslot is associated with asuperframe; and the method further comprises, after the first timeslot,transitioning the device to a low power mode for a remainder of thesuperframe.